The image above provided by the Harvard-Smithsonian Center for Astrophysics shows artist's renderings of planets Kepler-20e and Kepler-20f compared with Venus and the Earth. Scientists have found the two Earth-sized planets orbiting a distant star, an encouraging sign for prospects of finding life elsewhere.

The discovery shows that such planets exist and that they can be detected by the Kepler spacecraft, said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. They’re the smallest planets found so far outside the solar system. Scientists are seeking Earth-sized planets as potential homes for extraterrestrial life, said Fressin, who reports the new findings in a paper published online Tuesday, Dec. 30, 2011 by the journal Nature.